/*
 * Copyright (c) 2011-2012 Alexander Dubu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * o  Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * o  Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * o  Neither the name Axil nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

package axil.engine.access;

import axil.api.Context;
import axil.api.access.Accessor;


/**
 * An accessor for extracting a root element from the context.
 */
class ContextAccessor implements Accessor {
	private String ident;


	ContextAccessor(String ident) {
		this.ident = ident;
	}


	/**
	 * Access the field or object represented by this accessor object.
	 *
	 * @param context
	 * 	The context where the root object of an access path resides. The context
	 * 	given is never null. The context may, or may not, actually contain the
	 * 	desired object.
	 *
	 * @param parent
	 * 	The parent object, if any, from the previous (left hand) element of
	 * 	a compound identifier. For example, in the compound identifier
	 * 	"Shopping Cart.Items", when "Items" is accessed, the parent if the value
	 * 	of "Shopping Cart" extracted from the context. A null value is given
	 * 	when accessing a simple identifier or the root object in a compound
	 * 	identifier.
	 *
	 * @return
	 * 	Returns a null value if the field or object is null. Throws an exception
	 * 	if the field or object simply does not exist.
	 */
	public Object access(Context context, Object parent) {
		return context.get(ident);
	}
}
